Electromagnetic relays



June 18, 1968 I FLAHL'BERG 3,389,354

ELECTROMAGNETI C RELAY S Filed Dec. 13, 1965 INVENTOR. Cum- Fae 1mm ML-BERG BY Ham MWL TTOR NGYi United States Patent 3,389,354 ELECTROMAGNETIC RELAYS Curt Fredrik Ahlberg, Bromma, Sweden, assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden Filed Dec. 13, 1965, Ser. No. 513,483 Claims priority, application Sweden, Mar. 6, 1965, 2,948/ 65 3 Claims. (Cl. 335-248) ABSTRACT OF THE DISCLOSURE An electromagnetic relay in which the movement of the armature into and out of its position of attraction is damped or cushioned by interposing a flexible member which when the armature moves toward the core softens the impact thereof upon the core by spring action and which when the armature moves away from the core accelerates the initial armature movement and causes a more uniform decrease of the magnetic field then acting upon the armature.

A characteristic of electromagnetic relays, for example telephone relays, of a conventional design is that the movement of the armature is markedly irregular having a considerable increase of velocity at the end of the movement, upon release as well as upon attraction. Particularly with electromagnetic relays which should be quick to attract or release and therefore are supplied with great power or are designed with a magnet core having small eddy current losses, the final velocity of the armature will be so great that the striking against the magnet core upon attraction respectively against the yoke upon release is followed by rebounding and spring vibrations. These phenomena cause wear on parts that are movable relatively to each other, such as armature bearing and contacts, and cause furthermore both acoustical, mechanical and electrical disturbances in those, means of which the relay is a component.

The present invention has for a purpose to reduce by means of. simple means the velocity of motion of the armature at the end of the movement to so low a value that the impacts will cause no danger. This is achieved by means of a resilient residual plate located in the air gap between the armature and the magnet core, so arranged, that the resilient residual plate upon attraction during the last part of the movement of the armature increases the load of the armature and upon release hastens the starting of the releasing movement, so that the movement of the armature is controlled by the decreasing magnetic field.

The invention will be described below with reference to the enclosed drawings, FIGS. 1-3.

FIG. 1 shows a telephone relay with a residual plate according to the invention.

FIG. 2 shows the residual plate as seen from the pole end of the core in the-air gap.

FIG. 3 shows an embodiment of the residual plate.

FIG. 1 shows an angularly bent yoke 1 which carries a coil assembly 2 consisting of an iorn core 211, a coil 2b and end plates 2c, 2d. The yoke further carries an armature 3 and a contact spring assembly 5. The armature 3 is provided with a residual plate or strip 4 and a lever 31:. Initially, the effect of the residual plate 4 will be left out of consideration.

-When the magnet coil 2b is connected in a circuit, the magnetic field of the core 2a will rise comparatively slowly and irregularly due to inductance, eddy currents, the load, and the change of the air gap during the attraction of the armature. After the magnetic field has been built-up to the 3,389,354 Patented June 18, 1968 extent that the attractive power of the magnet is greater than the spring load 5, the armature 3 will accelerate swiftly and thus strike very hard against the core 2b. Hence the armature and the contact springs will begin to vibrate in a not desirable manner.

Upon release of the relay the armature is held a short while due to eddy currents in the iron core, the armature and the yoke and generally also due to a current flow from the magnet coil to a resistance connected in parallel with the magnet coil, for example for spark extinction. The magnetic field disappears comparatively swiftly and, when the attractive power of the armature becomes less than the spring load, the armature will release and the air gap will increase. Hereby the magnetic field decreases very swiftly and in spite of a voltage being induced in the coil 2b, which voltage may increase the current through the magnet coil, the armature will make a strongly accelerating movement until the lever 3a strikes against the yoke 1. Hereby the armature often bounces back and actuates again the contact spring assembly 5. Such a rebounding and all the contact vibrations arising upon the release, are undesirable :phenomena.

The acceleration of the armature upon operation may be decreased by arranging the total spring load for example by adding additional springs to assembly 5 or by separate springs so that the load increases in accordance with the increase of the magnetic field. Upon release it is difficult to avoid bounces and vibrations, especially if the release is to be swift. The armature is held until the spring load becomes predominant and hereby the magnetic energy has been substantially consumed and therefore the release step after the armature has begun .to move, has occurred very swiftly.

The residual plate or strip 4 is according to the invention resilient. Thus upon operation, a soft striking is obtained and a more or less complete balance is achieved between the attractive power of the armature and the sum of the counter force of the load and of the residual plate in operated condition. The release of the armature thus starts as soon as the magnetic field begins to decrease and the magnetic field will control the movement of the armature during the whole release time. Hence, the release time does not increase as happens with such known methods as slow action by means of copper rings or parallel-connected resistances, but the time of the movement of the armature is extended to encompass all the time that is needed for the disappearing of the field, in-

to FIG. 1 the point of the angle rests against the arma- I ture.

According to FIG. 3 the armature 3 is equipped with two residual plates 4a, 4b placed one on the other. The two residual plates are angularly bent and resilient. The angular point of plate 4a rests against the armature and the angular point of the second plate 4b is turned against the core 2a. The shanks of the residual plates rest against each other and the longer shanks are fastened to the armature with joint rivets close to the bearing of the armature. With this embodiment, wear caused by sliding along the pole surface of the core in the air gap, is avoided.

In order that the residual plates should not unnecessarily increase the non-magnetic gap between the armature and the iron core, at least one residual plate in FIG.

3, for example 4a, is made of magnetic material. If the abutment area between armature and the core is resilient so that balance arises between the magnetic attractive power and the spring load, both residual plates may be make of magnetic material.

I I claim:

1. An electromagnetic relay comprising in combination: a yoke; a core supported on the yoke; an exciting coil supported by the core and encompassing the same; a stationarily mounted contact spring load means; an armature pivotally supported by the yoke, said armature coacting with said load means so as to be urged by the spring action thereof into a rest position defining an air gap between the core and the armature, exitation of said coil causing attraction of the armature into an attracted position against the spring action of the load means; and a yieldable damping member partly bridging said air gap in the rest position of the armature, said damping member being in the form of an elongate springy plate having two portions defining an obtuse angle therebetween, one of said portions being secured on one end to the armature resting with its length flatly upon the same on the side thereof facing the core and the other portion of the plate extending at said obtuse angle into said air gap and toward the core, the other of said portions engaging'the armature when the same is magnetically attracted for movement toward the core whereby the counteracting force exerted by said other portion upon the armature movement increases from zero prior to the engage- 4.. ment of said other portion with the core to a magnitude such that said counteracting force in conjunction with the also counteracting force of the load means balances the force of the magnetic attraction thus cushioning the impact of the armature against the core and that upon release of the armature by a decay of the force of the magnetic attraction the spring forces stored in said other portion of the springy plate and in the load means accelerate the return movement of the armature toward its rest position. 2. An electromagnetic relay according to claim 1 wherein said springy plate is made of magnetic material.

3. An electromagnetic relay according to claim 1 wherein a second springy plate having two portions defining an obtuse angle therebetween is disposed upon the first springy plate in opposition to the angle defined by the portions of said plate and secured to the armature at the end of one of its portions.

References Cited UNITED STATES PATENTS $148,313 9/ 1964 Hancock 335-271 X 3,207,961 9/1965 Cohr 335--274 X FOREIGN PATENTS 525,107 5/1931 Germany.

42,368 1/ 1938 Netherlands.

BERNARD A. GILHEANY, Primary Examiner.

GEORGE HARRIS, Examiner. 

